*2.3. Effect of Composite Edible Coatings on Firmness*

The firmness of roots and vegetables is also an indicative quality parameter significant for consumer acceptance. The firmness of the control sample decreased throughout the storage period from 341.96 to 254.30 N, whereas CH- and SA + C-coated samples retained their hardness until day 12 (Figure 3). After 16 days of storage, a slight decrease in firmness was observed in Ch (from 384.42 to 314.19 N) and SA + C (411.21 to 306.02 N). However, no noticeable decrease was observed for the ChCSA-coated samples, indicating the beneficial and synergetic effect of multilayer gel coating over their single-layer film coatings. Previous studies reported that layer-by-layer coating enhanced the cell-wall structure and slowed down the cell degradation of fresh-cut products [35,36]. In addition, the combined antimicrobial and adhesion effects of Ch and SA inhibited the production and activities of microbial hydrolytic enzymes associated with cell wall components hydrolysis [11]. Moreover, the use of calcium chloride as a cross linking agent in ChCSA could have further enhanced firmness of coated samples [24].

**Figure 2.** The effect of single-layer and gel coatings on the percentage of weight loss of fresh-cut purple sweet potatoes. Vertical bars represent means and standard deviation. Bars with different alphabets within the same storage day (lower case) or same treatment group at different storage days (upper case) are significantly different (Tukey's HSD Test, *p ≤* 0.05). **Figure 2.** The effect of single-layer and gel coatings on the percentage of weight loss of fresh-cut purple sweet potatoes. Vertical bars represent means and standard deviation. Bars with different alphabets within the same storage day (lower case) or same treatment group at different storage days (upper case) are significantly different (Tukey's HSD Test, *p* ≤ 0.05). *Gels* **2022**, *8*, x FOR PEER REVIEW 5 of 14

#### *2.4. Effect of Composite Edible Coatings on Microbial Growth 2.4. Effect of Composite Edible Coatings on Microbial Growth*

Microbial contamination is the major reason for the deterioration of fresh-cut products. The presence and growth of microorganisms during product storage and distribution affects food quality and safety [5]. However, some edible coatings have shown barrier properties, inhibiting their proliferation in coated foods [35]. Notably, the application of coatings reduced the initial population of aerobic bacteria (Figure 4) and total fungi (Figure 5). However, an increase in bacteria (3.48 log CFU/mL in CON) and fungi (up to ~4.57 Microbial contamination is the major reason for the deterioration of fresh-cut products. The presence and growth of microorganisms during product storage and distribution affects food quality and safety [5]. However, some edible coatings have shown barrier properties, inhibiting their proliferation in coated foods [35]. Notably, the application of coatings reduced the initial population of aerobic bacteria (Figure 4) and total fungi (Figure 5). However, an increase in bacteria (3.48 log CFU/mL in CON) and fungi (up to

log CFU/mL in CON) were observed in samples at the end of storage. However, all coated samples showed lower microbial concentration. For instance, after 16 days of storage,

be attributed to the intrinsic bacteriostatic and fungistatic characteristics of chitosan, combined with the oxygen barrier properties of Ch and SA coatings which limited oxygen

**Figure 4.** The effect of single-layer and gel coatings on the aerobic bacteria on fresh-cut purple sweet potatoes. Vertical bars represent means and standard deviation. Bars with different alphabets within the same storage day (lower case) or same treatment group at different storage days (upper case)

Storage Time (days) 0 4 8 12 16

Bc

Ab

AaBab

Cc

Ba

Aab

Cb

Db

Ba Ca Ca

requirement for microbial proliferation [3,5]

Aerobic Bacteria (log CFU/ml)

0

Aa Aa Aa

CON Ch SA+C ChCSA

1

2

Ab

3

4

5

are significantly different (Tukey's HSD Test, *p ≤* 0.05).

Ab

Aa Aa

Aa

~4.57 log CFU/mL in CON) were observed in samples at the end of storage. However, all coated samples showed lower microbial concentration. For instance, after 16 days of storage, ChCSA-coated samples had aerobic bacteria and total fungi counts of 2.44 log CFU/mL, and 2.37 log CFU/mL, respectively. The antimicrobial properties of ChCSA coatings could be attributed to the intrinsic bacteriostatic and fungistatic characteristics of chitosan, combined with the oxygen barrier properties of Ch and SA coatings which limited oxygen requirement for microbial proliferation [3,5] log CFU/mL in CON) were observed in samples at the end of storage. However, all coated samples showed lower microbial concentration. For instance, after 16 days of storage, ChCSA-coated samples had aerobic bacteria and total fungi counts of 2.44 log CFU/mL, and 2.37 log CFU/mL, respectively. The antimicrobial properties of ChCSA coatings could be attributed to the intrinsic bacteriostatic and fungistatic characteristics of chitosan, combined with the oxygen barrier properties of Ch and SA coatings which limited oxygen requirement for microbial proliferation [3,5]

**Figure 3.** The effect of single-layer and gel coatings on the flesh firmness of fresh-cut purple sweet potatoes. Vertical bars represent means and standard deviation. Bars with different alphabets within the same storage day (lower case) or same treatment group at different storage days (upper case)

Ba

Storage Time ( days) 0 4 8 12 16

BbBbAb

Ba

BbBbcAc

Aa AabAab

Ab

Microbial contamination is the major reason for the deterioration of fresh-cut products. The presence and growth of microorganisms during product storage and distribution affects food quality and safety [5]. However, some edible coatings have shown barrier properties, inhibiting their proliferation in coated foods [35]. Notably, the application of coatings reduced the initial population of aerobic bacteria (Figure 4) and total fungi (Figure 5). However, an increase in bacteria (3.48 log CFU/mL in CON) and fungi (up to ~4.57

*Gels* **2022**, *8*, x FOR PEER REVIEW 5 of 14

are significantly different (Tukey's HSD Test, *p ≤* 0.05).

Firmness (N)

200

300

400

500

<sup>600</sup> CON

Ca Cbc

Ch SA+C ChCSA

Cc

Aab

BCa Bab Cc Abc

*2.4. Effect of Composite Edible Coatings on Microbial Growth*

**Figure 4.** The effect of single-layer and gel coatings on the aerobic bacteria on fresh-cut purple sweet potatoes. Vertical bars represent means and standard deviation. Bars with different alphabets within the same storage day (lower case) or same treatment group at different storage days (upper case) are significantly different (Tukey's HSD Test, *p ≤* 0.05). **Figure 4.** The effect of single-layer and gel coatings on the aerobic bacteria on fresh-cut purple sweet potatoes. Vertical bars represent means and standard deviation. Bars with different alphabets within the same storage day (lower case) or same treatment group at different storage days (upper case) are significantly different (Tukey's HSD Test, *p* ≤ 0.05). *Gels* **2022**, *8*, x FOR PEER REVIEW 6 of 14

**Figure 5.** The effect of single-layer and gel coatings on the yeast and mold on fresh-cut purple sweet potatoes. Vertical bars represent means and standard deviation. Bars with different alphabets within the same storage day (lower case) or same treatment group at different storage days (upper case) are significantly different (Tukey's HSD Test, *p ≤* 0.05). **Figure 5.** The effect of single-layer and gel coatings on the yeast and mold on fresh-cut purple sweet potatoes. Vertical bars represent means and standard deviation. Bars with different alphabets within the same storage day (lower case) or same treatment group at different storage days (upper case) are significantly different (Tukey's HSD Test, *p* ≤ 0.05).
